Speaking of eel-like engineer gobies, I'd advise strongly against getting one. Engineer gobies get large pretty fast, and they plague nitrate levels of tanks. My engineer goby became 10 inches long and has dug up over 80% of my tank. He digs so much my LR structures shift by inches, he has built 8" piles of LS, and he has built piles of sand right into filters and powerheads, messing up both. He has covered the bottom of my heater so much I had to move it twice. And worst of all, he destroys the point of having a sand bed. By having 80% of the sand churned up every week or so it decimates the denitrification properties of the sand bed, and it also releases toxins from the lower sand bed back into the tank. Even with meticulous care in my first tank, my nitrate levels have never been under control, courtesy of my friend the engineer goby.
But, he does look like an eel: